The present invention pertains to a patellar prosthesis and to a method of surgically implanting the same.
Prosthetic replacement of the patella has been known for some time. The patella is a small triangular shaped bone, commonly referred to as the kneecap, and has a posterior surface which has a transversely extending crest which divides the surface into a medial and a lateral facet which bear, respectively, on the femoral condyles. Trauma, degenerative changes or disease may cause this natural articulating surface to degenerate causing severe pain, and/or immobility of the knee joint. In such cases, particularly where more conservative methods of treatment fail, the implantation of a prosthesis to replace the degenerated natural articulating surface of the patella with an artificial surface is indicated.
Such prostheses are known in the art. For example, U.S. Pat. No. 3,927,423 discloses a patella implant formed of a resilient material, silicone rubber, which is sutured in place onto a flat resection of the patella posterior surface to provide an artificial articulating surface.
The use of a rigid patellar prosthesis is also known. For example, see the article "Some Aspects of Prosthetic Replacement of The Patella" by the inventor of the present invention in Orthopaedic Review, Volume V, No. 11, November 1976, pages 39-42. At page 40 of the cited article, there is shown a prior patellar prosthesis which comprises a rigid body having one side providing a convex articulating surface and an opposite side which is recessed somewhat and in which a stem of generally rectangular cross section is positioned. The stem extends outwardly and terminates in an enlarged cross section portion. Such prostheses are rigid, usually being made of a stainless steel for strength and durability. This results in one difficulty encountered with the prosthesis illustrated in the article, in that the thickness of the body portion and stem results in a device which is quite heavy for its size. As a consequence, patients in whom it was implanted required a good quadri ceps muscular reserve in order to be able to manipulate the knee joint with facility.
Another shortcoming of the described prosthesis is that the flat or planar configuration of the seating rim in side profile and the generally rectangular cross section of the anchoring stem failed to adequately secure the implanted prosthesis against shifting and/or rotation. This problem was aggravated by the heaviness of the device.
It is accordingly an object of the present invention to provide a novel patellar prosthesis of rigid construction which is light in weight and which may be implanted in the patella posterior surface in a manner in which it is secured against shifting or rotation.
It is another object of the present invention to provide a light weight patellar prosthesis of novel design and a method of implanting the same.
Other objects and advantages of the present invention will become apparent from the following description thereof.